1. Field of the Invention
The present invention relates to color processing for converting image data of an input device into that for an output device.
2. Description of the Related Art
FIG. 1 shows the concept of color matching.
Input RGB data is converted into XYZ data of a device-independent space using an input profile 1. The XYZ data is converted into CMYK data of a color space depending on an output device using an output profile 2.
Conversion using the output profile 2 includes gamut mapping processing and conversion processing that converts the XYZ data which has undergone the gamut mapping into CMYK data. The output device cannot express colors outside the color reproduction range (to be referred to as a “gamut” hereinafter). Hence, the gamut mapping processing maps an input color to a color within the gamut of the output device.
In color matching, a reference white point and ambient light are fixed. For example, an ICC (International Color Consortium) profile specifies a profile connection space (PCS) in D50. For this reason, when an input document or print is viewed under a light source with the D50 characteristic, accurate color reproduction is guaranteed. However, under light sources with other characteristics, accurate color reproduction is not guaranteed.
The color reproduction characteristic of a printer changes depending on ambient conditions such as a temperature, humidity, and the like when the printer is in operation, and the aging it has suffered so far. The printer requires calibration for calibrating the conversion processing conditions according to the changed color reproduction characteristic.
Likewise, a scanner also requires calibration before accurate scanning is to be done, due to ambient conditions such as a temperature, and the like when the scanner is in operation, and the aging it has suffered so far.
The conversion conditions of color matching must be calibrated according to a change in color reproduction characteristic of the device. However, it is not easy to create the conversion conditions since data indicating the relationship between color signals of the color space of the device whose color reproduction characteristic has varied, and those of the device-independent color space must be obtained again.